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if only i could figure out who's numbers to better trust- an accredited state university physics dept., or some anonymous guy on the internet...hmmmm...:shrug: http://www.unh.edu/p2/biodiesel/article_alge.htmlII. Large scale productionThere are two steps that would need to be taken for producing biodiesel on a large scale - growing the feedstocks, and processing them into biodiesel. The main issue that is often contested is whether or not we would be able to grow enough crops to provide the vegetable oil (feedstock) for producing the amount of biodiesel that would be required to completely replace petroleum as a transportation fuel. So, that is the main issue that will be addressed here. The point of this article is not to argue that this approach is the only one that makes sense, or that we should ignore other options (there are some other very appealing options as well, and realistically it makes more sense for a combination of options to be used). Rather, the point is merely to look at one option for producing biodiesel, and see if it would be capable of meeting our needs.
One of the important concerns about wide-scale development of biodiesel is if it would displace croplands currently used for food crops. In the US, roughly 450 million acres of land is used for growing crops, with the majority of that actually being used for producing animal feed for the meat industry. Another 580 million acres is used for grassland pasture and range, according to the USDA's Economic Research Service. This accounts for nearly half of the 2.3 billion acres within the US (only 3% of which, or 66 million acres, is categorized as urban land). For any biofuel to succeed at replacing a large quantity of petroleum, the yield of fuel per acre needs to be as high as possible. At heart, biofuels are a form of solar energy, as plants use photosynthesis to convert solar energy into chemical energy stored in the form of oils, carbohydrates, proteins, etc.. The more efficient a particular plant is at converting that solar energy into chemical energy, the better it is from a biofuels perspective. Among the most photosynthetically efficient plants are various types of algaes.
The Office of Fuels Development, a division of the Department of Energy, funded a program from 1978 through 1996 under the National Renewable Energy Laboratory known as the "Aquatic Species Program". The focus of this program was to investigate high-oil algaes that could be grown specifically for the purpose of wide scale biodiesel production1. The research began as a project looking into using quick-growing algae to sequester carbon in CO2 emissions from coal power plants. Noticing that some algae have very high oil content, the project shifted its focus to growing algae for another purpose - producing biodiesel. Some species of algae are ideally suited to biodiesel production due to their high oil content (some well over 50% oil), and extremely fast growth rates. From the results of the Aquatic Species Program2, algae farms would let us supply enough biodiesel to completely replace petroleum as a transportation fuel in the US (as well as its other main use - home heating oil) - but we first have to solve a few of the problems they encountered along the way.
NREL's research focused on the development of algae farms in desert regions, using shallow saltwater pools for growing the algae. Using saltwater eliminates the need for desalination, but could lead to problems as far as salt build-up in bonds. Building the ponds in deserts also leads to problems of high evaporation rates. There are solutions to these problems, but for the purpose of this paper, we will focus instead on the potential such ponds can promise, ignoring for the moment the methods of addressing the solvable challenges remaining when the Aquatic Species Program at NREL ended.
NREL's research showed that one quad (7.5 billion gallons) of biodiesel could be produced from 200,000 hectares of desert land (200,000 hectares is equivalent to 780 square miles, roughly 500,000 acres), if the remaining challenges are solved (as they will be, with several research groups and companies working towards it, including ours at UNH). In the previous section, we found that to replace all transportation fuels in the US, we would need 140.8 billion gallons of biodiesel, or roughly 19 quads (one quad is roughly 7.5 billion gallons of biodiesel). To produce that amount would require a land mass of almost 15,000 square miles. To put that in perspective, consider that the Sonora desert in the southwestern US comprises 120,000 square miles. Enough biodiesel to replace all petroleum transportation fuels could be grown in 15,000 square miles, or roughly 12.5 percent of the area of the Sonora desert (note for clarification - I am not advocating putting 15,000 square miles of algae ponds in the Sonora desert. This hypothetical example is used strictly for the purpose of showing the scale of land required). That 15,000 square miles works out to roughly 9.5 million acres - far less than the 450 million acres currently used for crop farming in the US, and the over 500 million acres used as grazing land for farm animals.
The algae farms would not all need to be built in the same location, of course (and should not for a variety of reasons). The case mentioned above of building it all in the Sonora desert is purely a hypothetical example to illustrate the amount of land required. It would be preferable to spread the algae production around the country, to lessen the cost and energy used in transporting the feedstocks. Algae farms could also be constructed to use waste streams (either human waste or animal waste from animal farms) as a food source, which would provide a beautiful way of spreading algae production around the country. Nutrients can also be extracted from the algae for the production of a fertilizer high in nitrogen and phosphorous. By using waste streams (agricultural, farm animal waste, and human sewage) as the nutrient source, these farms essentially also provide a means of recycling nutrients from fertilizer to food to waste and back to fertilizer. Extracting the nutrients from algae provides a far safer and cleaner method of doing this than spreading manure or wastewater treatment plant "bio-solids" on farmland.
These projected yields of course depend on a variety of factors, sunlight levels in particular. The yield in North Dakota, for example, wouldn't be as good as the yield in California. Spreading the algae production around the country would result in more land being required than the projected 9.5 million acres, but the benefits from distributed production would outweigh the larger land requirement. Further, these yield estimates are based on what is theoretically achievable - roughly 15,000 gallons per acre-year. It's important to point out that the DOE's ASP that projected that such yields are possible, was never able to come close to achieving such yields. Their focus on open ponds was a primary factor in this, and the research groups that have picked up where the DOE left off are making substantial gains in the yields compared to the old DOE work - but we still have a ways to go. But, consider that even if we are only able to sustain an average yield of 5,000 gallons per acre-year in algae systems spread across the US, the amount of land required would still only be 28.5 million acres - a mere fraction still of the total farmland area in the US.
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